There have conventionally been developed various types of backlight units for supplying light to a liquid crystal display panel (a non-light-emitting display panel). Backlight units typically include a light source that emits light. For example, the backlight unit 149 disclosed in Patent Document 1 has the LED (light emitting diode) 112 mounted on the mounting substrate 111 as shown in the sectional view of FIG. 25. The LED 112 emits light that enters the light guide plate 141 to travel toward the liquid crystal display panel 159 via the reflection sheet 142 and a group of optical sheets 146.
Such light is generated by driving the LED 112, but when the LED 112 is driven to generate light, heat is generated as well. The thus generated heat deteriorates the quality of the LED 112 (for example, the light emitting efficiency of the LED 112 is degraded or the life of the LED 112 is shortened). The heat of the LED 112 is also transferred to the mounting substrate 111, and the heat causes early deterioration or warp of the mounting substrate 111.
In order to prevent such defects caused by heat, in the backlight unit 149 described in Patent Document 1, the mounting substrate 111 on which the LED 112 is mounted is put in contact with the heat sink substrate 172 via the heat dissipation sheet 171. With this structure, heat of the LED 112 does not stay in the LED 112 or the mounting substrate 111 but escapes to the heat dissipation sheet 171 and to the heat sink substrate 172.
If the backlight unit 149 is used for a long time, however, the heat generated therein cannot be dealt with by heat dissipation merely by means of the heat dissipation sheet 171 and the heat sink substrate 172, and the mounting substrate 111 may, for example, warp in the worst case. To prevent this, in the backlight unit 149, the LED 112 and the mounting substrate 111 are placed between the light guide plate 141 and the heat sink substrate 172, and further, the mounting substrate 111 is placed between the housing 125 and the heat sink substrate 172 of the backlight unit 149.
The exploded perspective view of FIG. 26 and the sectional view of FIG. 27 show a backlight unit 149 as an example of backlight units other than that disclosed in Patent Document 1, and according to this backlight unit 149, it is possible to fasten a housing 121 and a mounting substrate 111 of the backlight unit 149 together with screws 173 (here, FIG. 27 is a sectional view taken along line a-a′ in FIG. 26, and a liquid crystal display panel 159 is additionally illustrated therein).    Patent Document 1: JP-A-2006-11242